16 Jan 20
https://phys.org/news/2020-01-transparency-crystals-ultrahigh-piezoelectricity.html.
So does there have to be a permanent AC applied to keep the effect going or is the AC a prep stage? And there was no mention of either voltage levels or frequency.
The graphic shows a sawtooth wave with apparently very low frequency but it could be anything.
My guess is after the appropriate number of AC cycles it is ready to be used as a piezo crystal.
Article was a bit vague on operability.
My buddy Ray Scudero and I played with piezo pickups for musical instruments one summer in Jerusalem and found some interesting things about regular ones, like the ones in sonalerts.